1. Field of the Invention
The invention relates to an LCD displays or a semimanufactured goods therefor for use with terminal devices such as notebook type personal computers (PCs) and cellular phones, and more particularly to the methods and apparatuses of measuring viewing angle characteristics and positional characteristics of luminance of such products.
2. Description of the Prior Art
A typical prior art apparatus for measuring angular distribution of luminance (also referred to as luminance distribution measurement apparatus) is disclosed in FIGS. 15, 16, and 17 of Japanese Patent Early Publication of the 6-94515. The apparatus shown in FIG. 15 includes a radiant object in the form of liquid crystal display (LCD) panel 41 having radiant areas (pixels), a light source 42, and a photometer 43 for measuring the intensity of light. The apparatus shown in FIG. 16 includes a mounting table 44, a lens 45, and an array of charge coupled device (CCD) 46. The apparatus shown in FIG. 17 includes a CCD array 47. In what follows like reference numerals refer to like or corresponding parts throughout the specification.
In the prior art apparatus shown in FIG. 15, angular distribution of luminance or viewing angle characteristic of luminance is obtained by measuring the luminance of a pixel 41a, i. e. intensity of radiation from the pixels 41a, of the LCD panel 41 which is illuminated by the light source 42. The measurement is done by rotating the photometer 43 about the pixel 41a in the tangential direction perpendicular to the radiation and measure the intensity of the radiation by the photometer 43.
In the prior art apparatus shown in FIG. 16, the beams of light radiated from the pixel 41a are collimated into parallel beams of light by a lens 45 and supplied to the CCD array 46. The directional characteristic of a radiant pixel 41a is obtained in terms of positional characteristic of the information collected on the CCD array 46.
The apparatuses shown in FIGS. 15 and 16 are designed for the measurement of a characteristic angular distribution of a pixel. Apparatuses such as shown in FIG. 17 are widely used in LCD factories as means for evaluating linear defects and uneven luminance of LCD panels. The apparatus shown in FIG. 17 uses a lens to condense the light that emerges from a pixel 41a onto a CCD array 47.
In the conventional apparatus shown in FIG. 15, it is necessary to make the aperture of the lens sufficiently small in order to attain a high resolution, since the angular resolution of a convex lens 45 in photometer 43 is determined by the aperture of the lens. The apparatus shown in FIG. 16 is handy in that the CCD array 46 need not be moved for the measurement. However, if the pixel density is increased in an attempt to raise the resolution, the average intensity of light per one pixel is disadvantageously decreased. Furthermore, a large aperture lens is needed to obtain a better viewing-angle characteristic, which makes the apparatus costly.
The prior art apparatus of FIG. 17 has a further disadvantage that accurate information of pixels cannot be obtained due to the fact that the information, obtained in the form of image on the CCD array 47, includes angular characteristics of the pixels. Unevenness of luminance of a LCD panel due to angular luminance characteristic of each pixel is best evaluated by comparing the parallel radiation beams emitted from the comparing pixels in the same direction. However, in the apparatus of FIG. 17, the information carried by the light from the central region of the LCD panel onto the CCD array is greatly affected by the information carried by the light from peripheral regions of the LCD panel. (This can be seen from the fact that the vertical angle xcfx861 of the beam starting from a peripheral region is greater than the corresponding angle xcfx860 from the central region, xcfx861 greater than xcfx860) . As a result, if the angular distribution of luminance is the same in the central and the peripheral regions of the LCD panel, the apparatus of FIG. 17 can provide different CCD outputs for the two regions. Hence, the apparatus of FIG. 17 has a drawback that must be overcome if it is usable as an apparatus for evaluating unevenness of pixels.
It is therefore an object of the invention to provide an improved apparatus attaining a desired resolution in the measurement of angular luminance distribution by increasing the intensity of light falling on each CCD pixel as much as possible, thereby preventing the loss of sensitivity of the CCD device caused by increasing CCD density on the CCD device and preventing loss of the accuracy of the measurement due to condensation effect of the condensing lens.
It is another object of the invention to provide an improved method of measuring the angular distribution of luminance and an apparatus therefor, without loosing the resolution in the measurement.
It is a further object of the invention to provide a method of obtaining accurate data and an apparatus therefor through a correction of the relative position of a condensing lens or a mirror condensing the light from radiant areas when the relative position is changed.
It is a still further object of the invention to provide a measurement apparatus equipped with a light receiving element such as a condensing lens or mirror and a mechanism for moving an imaging device, making expendable conventional large aperture condensing lenses and reducing the number of imaging elements.
It is a still further object of the invention to provide a high-precision apparatus capable, through an appropriate data processing, of obtaining information on the angular dependency of luminance of a radiant area of a panel as viewed from an arbitrary direction by taking account of the radiation not only from particular pixels but from all the pixels of the panel, so that the invention enables inspection of the panel for defects and unevenness of luminance as viewed from an arbitrary direction.
To the accomplishment of the above objects of the invention, there is provided an apparatus for measuring viewing-angle characteristic of luminance and positional characteristic (2-dimensional characteristic) of a radiant object under measurement, by moving a condensing device and an imaging device relative to said object, said condensing device condensing light from radiant area (hereinafter referred to as radiant area) of said radiant object and said imaging device forming thereon a real image of said area, said apparatus comprising:
a first mechanism for moving the light receiving elements of said condensing device while keeping constant the solid angle subtended by said light receiving element at said radiant area;
a second mechanism for moving said imaging device in association with said condensing device, while maintaining thereon said image of said radiant area;
a memory for storing a predetermined condensing function of angle of a beam of light emitted from a laser light source positioned at said radiant area and oriented in the direction at a given angle with respect to the optical axis of said condensing device, said condensing function, the variable of which is said angle of light beam with respect to optical axis, representing the measured intensity of the image formed on said imaging device by said beam of light;
a circuit for calculating the characteristic viewing angle dependent and potion dependent characteristic of luminance (hereinafter referred to as luminance characteristic) of said radiant area based on the data of said measurement and condensing function; and
a display device for displaying characteristics of said object and said distribution characteristic of said area evaluated.
In one embodiment of the apparatus of the invention, the condensing device may have light receiving elements in the form of a lens or a flat or concave mirror such that the lens condenses the light reflected by the mirror.
Other embodiments of the apparatus may further include a circuit for making a correction of the measurement, when the solid angle subtended by the light receiving element (lens or mirror) of the condensing device as viewed from the radiant area is changed by the movement of the condensing device, wherein the correction is given by the output of the imaging device measuring the luminance at a solid angle, divided by the output of the imaging device measuring the luminance at a reference solid angle.
A method of measuring viewing angle characteristic and positional characteristic of a radiant object of the invention, comprises steps of moving a condensing device and an imaging device relative to said radiant object so as to construct a real image of said radiant object on said imaging device, said method further comprising steps of:
moving the light receiving elements of said condensing device while keeping constant the solid angle subtended by said light receiving element as viewed from the radiant area;
moving said imaging device in association with said condensing device so as to form thereon the real image of said radiant area to measure the luminance thereof; and
calculating the viewing angle dependent and position dependent characteristic of luminance of said radiant area based on the viewing angle dependent luminance data measured by an imaging device and a condensing function of angle of a radiant beam with respect to the optical axis of said imaging device, said condensing function determined by measuring the intensity of the image formed on said imaging device through a condensing device by a beam of light emitted from a laser light source positioned at said radiant area to said imaging device.
The method of the invention further includes a step of making a correction when the solid angle subtended by the light receiving element (lens or mirror) of the condensing device as viewed from the radiant area of a radiant object is altered by the movement of the condensing device, wherein the output of the imaging device representing the directional luminance characteristic of the pixel in that moved direction as viewed from the area towards the center of the light receiving element is dived by the output obtained for the radiation emitted from the object in a specified direction.